Human herpesvirus-8 (HHV-8) is a gamma-2 herpesvirus and,like many other members of the subfamily, is associated with neoplasia, including B cell malignancies and endothelial cell angioproliferative diseases. One of the HHV-8 proteins implicated in viral pathogenesis is the viral G protein-coupled receptor (vGPCR) encoded by open reading frame (ORF) 74. The receptor effects cellular proliferation and transformation in vitro and tumorigenesis and angiogenesis in vivo. GPCRs in other herpesviruses, including murine gamma- herpesvirus-68 (MHV-68), have been demonstrated to play roles in virus lytic replication, both in culture and in vivo. Understanding the mechanisms and regulation of HHV-8 vGPCR signaling is therefore relevant to attempts to control virus replication and associated disease. Previous structure-function studies of vGPCR in this laboratory identified receptor residues involved in Ga coupling and selectivity, and enabled dissociation of Ga subclass-activated pathways. The aims of this proposal are (1) to extend our previous structure-function studies of HHV-8 vGPCR to characterize the structural requirements for GRK-mediated negative regulation of vGPCR signaling, and (2) to utilize engineered functionally altered vGPCR proteins to investigate the roles of particular signaling pathways and vGPCR-regulatory mechanisms in virus replication. These studies will, for the first time, address the function of vGPCR in virus lytic replication, and provide enabling data, technology and reagents for future studies of the role of vGPCR-activated pathways and control mechanisms in disease development in in vitro and in vivo models of KS.